There has been a progress in the technology to recover energies from heat sources in an intermediate or low temperature range lower than the temperature obtained by combustion of fuels such as heavy oil, petroleum oil, etc., and power generation by ocean thermal energy conversion, geothermal binary power generation, waste heat recovery power generation, solar thermal power generation, heating by a heat pump, heat exchange by a heat pipe, etc., have been practically used or tested.
As a working fluid to be used for such power generation, heat pumps, etc., water, a hydrocarbon such as propane or butane, a fluorocarbon such as trichlorofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12), chlorodifluoromethane (HCFC-22), trichlorotrifluoroethane (CFC-113) or dichlorotetrafluoroethane (CFC-114), or ammonia, may, for example, be known.
Ammonia and hydrocarbons have some restrictions in their commercial use in view of the safety problem such as toxicity, inflammability or corrosiveness or for such a reason that the energy efficiency is poor.
Many of fluorocarbons have merits such that they have little toxicity and are non-flammable and chemically stable, and various fluorocarbons having different normal boiling points are readily available, and thus, they are expected to be useful as working fluids, and evaluation and researches of fluorocarbons are being actively carried out.
However, among fluorocarbons, compounds containing chlorine atoms are considered to have a nature to remain in the environment or to have a relation to depletion of ozone layer, and their stepwise reduction and total ban are being endeavored. For example, chlorofluorocarbons (CFC) containing chlorine atoms and having all hydrogen atoms halogenated have already been completely banned in advanced countries like Japan, USA and European countries. Further, with respect to hydrochlorofluorocarbons (HCFC) containing hydrogen atoms, reduction towards the total ban in 2020 is being endeavored in advanced countries. Further, perfluorocarbons (PFC) and hydrofluorocarbons (HFC) contain no chlorine atom and therefore are free from an influence to ozone layer, but their influence to the global warming has been pointed out, and they are designated as compounds for global warming, the discharge of which to the atmosphere should be controlled.
As a compound or composition which is non-flammable and little influential over the environment, the following ones have been proposed.
(1) An azeotropic composition comprising a hydrofluoroether of the formula C2FnH(6-n)O (wherein n is from 2 to 5) and a hydrofluorocarbon of the formula CxFnH(2x+2-n) (wherein x is from 1 to 3, and n is from 2 to 7) (Patent Document 1).
(2) A hydrofluoroether of the formula CaFbH2a+2−bOc (wherein a is from 3 to 6, b is from 1 to 14, and c is 1 or 2) or a non-cyclic hydrofluorocarbon of the formula CdFeH2d+2−e (wherein d is from 4 to 6 and e is from 1 to 14) (Patent Document 2).
The hydrofluoroether in (1) has a low normal boiling point and a low critical temperature, and accordingly, in a case where such a compound is used as a working fluid, in power recovery by a Rankine cycle from an intermediate or high temperature heat source with a waste heat temperature exceeding 100° C., or with a heat pump intended to supply hot water at a withdrawal temperature of about 100° C., the operation pressure tends to be a high pressure, and at the same time, depending upon the operation conditions, a cycle exceeding the critical temperature will be formed. Therefore, there will be a problem such that the efficiency deteriorates, and the instruments tend to be expensive, such being poor in practical applicability.
Patent Document 2 discloses that the compound in (2) is useful for e.g. a refrigerant, a cleaning agent, aerosol propellant, a fire extinguisher, a blowing agent or a working fluid for power. And, in Patent Document 2, as the hydrofluoroether, CHF2CH2OCF2CF3 (347mcfEβγ) or CHF2OCH2CF2CF3 (347mcfEγδ) is, for example, mentioned.
However, in Patent Document 2, a centrifugal refrigerator is the sole example wherein the hydrofluoroether is used as a working fluid, and there is no disclosure about a specific performance in a Rankine cycle system or a heat pump cycle system.
Further, in Patent Document 2, the chemical name for 347mcfEβγ is disclosed to be “1,1,2,2-tetrafluoro-1-(2,2,2-trifluoroethoxy)-ethane”. However, as is evident from the following chemical formulae and the boiling points, 347mcfEβγ and 1,1,2,2-tetrafluoro-1-(2,2,2-trifluoroethoxy)-ethane (hereinafter sometimes referred to as HFE-347) are different compounds.
347mcfEβγ: CHF2CH2OCF2CF3, boiling point: 45.4° C.
HFE-347: CHF2CF2OCH2CF3, boiling point: 56° C.
Thus, the chemical name of 347mcfEβγ in Patent Document 2 is apparently erroneous, and the disclosure in Patent Document 2 does not suggest the possibility of HFE-347 as a working fluid.
Patent Document 1: JP-A-7-504889
Patent Document 2: JP-A-10-506926